1. Field of the Invention
The present invention relates generally to a gas turbine fuel system and more specifically to a gas turbine fuel system comprising a fuel oil distribution control system, a fuel oil purge system, a purging air supply system and a fuel nozzle wash system in which, fuel oil distribution is controlled to be done uniformly to a plurality of fuel nozzles with enhanced reliability of fuel distribution, and residual oil in fuel pipings and nozzles, when gas turbine operation is changed over to gas fuel from oil fuel, is purged effectively so that a load change caused by burning of the residual oil at the time of purging is prevented.
2. Description of the Prior Art
FIG. 9 is a block diagram-of an entire gas turbine fuel system comprising therein a fuel oil supply system, a fuel oil purge system, a purging air supply system and a compressor outlet wash system in the prior art. In FIG. 9, a combustor X comprises therein a plurality, about 20 pieces for example, of fuel nozzles X1, X2 disposed along an inner periphery thereof. The fuel nozzles X1 are supplied with fuel gas from a fuel gas supply system and the fuel nozzles X2 are supplied with fuel oil from a fuel oil supply system G. The gas and oil are changed over to either one thereof to be supplied into the combustor X for combustion. The fuel oil supply system G, as mentioned, is a system for supplying therethrough fuel oil and a fuel oil purge system H is a system for purging oil remaining in the piping system or fuel nozzles when the fuel is changed over to gas from oil. A purging air supply system J supplies therethrough a purging air into the fuel oil purge system H. A compressor outlet wash system K is a system for injecting water into a compressor outlet for washing this compressor outlet which communicates with the combustor. Description will be made further on each of the above systems.
The fuel oil supply system G will be described first. In the gas turbine, a stable combustion is required for a wide range of fuel flow rates from ignition to power output. Especially, in the low fuel flow rate range at the time of ignition etc., there is only a small differential pressure of the fuel nozzles in the combustor, which results in an unstable combustion. In recent gas turbines there are provided a large number of fuel nozzles, of about 20 pieces, and there arises an imbalance in the fuel flow rate due to the influence of the head difference between upper ones and lower ones of the fuel nozzles, which are vertically disposed. For this reason, a flow divider is provided so that fuel is divided to be supplied uniformly to each of the fuel nozzles. But this flow divider is not necessarily of a sufficient reliability, and troubles in the fuel system are thereby often caused.
FIG. 10 is a diagrammatic view of the fuel oil supply system G in the prior art. In FIG. 10, fuel oil is flow rate controlled by a flow control valve 11 to then flow through a piping 12 and enter a flow divider 80 to be divided there to flow through a plurality of pipings 82 of about 20 pieces and to be supplied into each of the fuel nozzles X2 of the combustor X. The gas turbine fuel nozzles X2 are disposed in about 20 pieces along a circumference and there is a head difference of about 4 m between the nozzles of upper positions and those of lower positions. This head difference produces an imbalance in the fuel flow rate, especially in the low fuel flow rate range at the time of ignition. For this reason, the flow divider 80 is provided, but this flow divider 80 is constructed such that a spiral shaft is disposed in a cylindrical body, and while this shaft is rotated, fuel oil flows into the cylindrical body to be divided to flow through each of the plurality of pipings 82 uniformly. A motor 81 is operated only during the operation start time for ensuring a smooth start of rotation of the flow divider 80.
FIG. 11 is a view showing a relation between load transition (fuel flow rate) and system differential pressure in the prior art gas turbine, wherein as load increases, fuel flow rate increases from gas turbine ignition time t0 to rated speed (no load) arrival time t1, and further to time t2 when the system differential pressure, including nozzle differential pressure, comes to a necessary nozzle differential pressure V1. That is, during the time T from t0 to t2, the system differential pressure does not reach the necessary nozzle differential pressure V1, but reaches V2 at time t2 to increase more thereafter. Accordingly, the nozzle differential pressure is low during the time shown by T, and if there is a head difference between the plurality of fuel nozzles, there occurs an imbalance of fuel flow rates between each of the fuel nozzles, hence the flow divider 80 is operated so that the imbalance of the fuel oil between each of the fuel nozzles may be eliminated. But this flow divider 80 has a very small gap between the inner rotational body and the stationary portion for its function, and this makes control of foreign matter difficult and has often been a cause of trouble in the fuel system.
Next, the fuel oil purge system H will be described. FIG. 12 is a diagrammatic view of the fuel oil purge system in the prior art at the time when the gas turbine fuel is changed over. In FIG. 12, numeral 1 designates a flow control valve in a fuel gas system, numeral 2 designates a piping therefor, numeral 3 designates a fuel gas distributor, which distributes the fuel gas to the plurality of fuel nozzles X1 and numeral 4 designates a plurality of pipings, which supply therethrough the fuel gas from the fuel gas distributor 3 to the respective fuel nozzles X1.
Numeral 11 designates a flow control valve in a fuel oil system, numeral 12 designates a piping therefor, numeral 13 designates a header, which distributes the fuel oil from the piping 12 to the plurality of fuel nozzles X2 and numeral 14 designates a plurality of pipings, which are connected to the header 13 and supply therethrough the fuel oil distributed by the header 13 to the respective fuel nozzles X2. Numeral 26 designates a purging air system piping, numeral 25 designates an opening/closing valve, numeral 23 designates a drain valve piping and numeral 24 designates an opening/closing valve therefor. Combustor X comprises therein the fuel nozzles X1, X2.
In the mentioned system so constructed, while the operation is done with the fuel oil being burned, the fuel oil flowing through the flow control valve 11 and the piping 12 is distributed by the header 13 to flow through the plurality of pipings 14 to the respective fuel nozzles X2. The fuel oil so distributed is injected into the combustor X from the fuel nozzles X2 for combustion.
When the operation is done with the fuel being changed over to gas from oil, the flow control valve 11 is closed and the fuel gas is led instead into the piping 2 to be supplied to the fuel nozzles X1 through the fuel gas distributor 3 and the piping 4. In this case, the previous fuel oil remains as it is in the pipings 12, 14, and this fuel oil, if left there, is carbonized to stick there, with a fear of causing blockage of the pipings and nozzles. Hence, it is necessary to remove such residual oil when the fuel is changed over to gas.
Thus, the opening/closing valve 25 is opened so that purging air 40 is led into the piping 12 from the purging air system piping 26. The purging air 40 enters the header 13 through the piping 12 to then flow through the pipings 14 to the fuel nozzles X2 to be blown into the combustor X. Thereby, the fuel oil which remains in the piping 12, header 13, pipings 14 and fuel nozzles X2 is all discharged into the combustor X. This purging of the residual oil is done while the operation is continued with the fuel gas being supplied and burned in the combustor X. But there is a considerable quantity of such residual oil itself in the piping 12, header 13, pipings 14 and fuel nozzles X2, and also there are provided a large number of the fuel nozzles X2, and the same number of the pipings 14 connected to the respective fuel nozzles X2. Accordingly, if the residual oil in these portions is all discharged into the combustor X and the operation is continued with the fuel gas so changed over, then the fuel oil so discharged into the combustor X burns so that the fuel increases beyond a planned supply value, which elevates the combustion temperature to cause a large load change. Hence, realization of a fuel oil purge system which does not cause such a load change has long been desired.
Next, the purging air supply system J will be described. In the recent gas turbine, there is realized an operation system wherein fuel is changed over to gas from oil, as mentioned above. This operation system comprises both the fuel oil system, and fuel gas system and it is necessary to purge fuel pipings and nozzles on the side not used. Especially in the fuel oil system, oil remains in the pipings and, if left as it is, is carbonized to stick there, and there is a fear of blockage of the pipings and nozzles.
FIG. 13 is a diagrammatic view of the purging air supply system J in the prior art gas turbine. In FIG. 13, numeral 110 designates a gas turbine, numeral 42 designates piping for taking out therethrough outlet air of an air compressor and numeral 90 designates an air cooler, which comprises therein a multiplicity of tubes communicating with the piping 42. Numeral 91 designates a motor for rotating a fan 92 to thereby supply air to the air cooler 90 and numeral 43 designates piping connecting to outlet of the air cooler 90. Numeral 93 also designates piping, which diverges from the piping 42 for obtaining air of the purge system, and numeral 94 designates a cooler using water 95 for cooling the air from the piping 93. Numeral 96 designates piping connected to an outlet of the cooler 94, numeral 97 designates a drain separator, numeral 98 designates piping connected to outlet of the drain separator 97, numeral 53 designates a pressure elevation compressor and numeral 99 designates piping connected to an outlet of the pressure elevation compressor 53. Numeral 100 designates a cooler using water 101 for cooling the air which has been heated to a high temperature by pressure elevation at the pressure elevation compressor 53 to an appropriate temperature as fuel nozzle purging air. Numeral 48 designates piping for supplying therethrough the air which has been cooled to the appropriate temperature as the purging air at the cooler 100.
In the mentioned system so constructed, the air of the compressor outlet of about 400xc2x0 C. is cooled at the air cooler 90 to about 200xc2x0 C. to 250xc2x0 C. to be supplied into the gas turbine 110 as rotor cooling air through the piping 43. A portion of the air of the compressor outlet diverges from the piping 42 and is led into the cooler 94 through the piping 93 to be cooled to about 130xc2x0 C. to then be sent to an inlet of the pressure elevation compressor 53. This air is removed of drainage by the drain separator 97 disposed between the pipings 96 and 98. Then the air is compressed to a predetermined pressure at the pressure elevation compressor 53 and its temperature is also elevated to about 200xc2x0 C. This air of about 200xc2x0 C. is led into the cooler 100 through the piping 99 to be cooled to about 150xc2x0 C., which is appropriate for purging, and is then supplied to each of the fuel systems through the piping 48 as the purging air.
Thus, in the purging air supply system, as the inlet temperature of the pressure elevation compressor 53 becomes high there is provided the cooler 94 for cooling the compressor outlet air of about 400xc2x0 C. to about 100xc2x0 C. to 130xc2x0 C. Also, as the air, when compressed at the pressure elevation compressor 53, is heated to about 200xc2x0 C., it is cooled again at the cooler 100 to about 150xc2x0 C. In this kind of system, therefore, there are needed the coolers 94, 100 or the like, which requires large facilities and space therefor. Hence, it has been needed to improve these shortcomings and to attain cost reduction.
Next, the compressor outlet washing system K will be described. FIG. 14 is, a diagrammatic view of the compressor outlet wash system in the prior art. In FIG. 14, letter X designates a combustor, numeral 112 designates a compressor outlet and numeral 113 designates a manifold for distributing wash water in an annular form, as described later. Numeral 114 designates a plurality of wash nozzles, which are provided along a periphery of the manifold 113 for injecting therefrom wash water into the compressor outlet 112. Numeral 11 designates a flow control valve for fuel oil, numeral 12 designates a piping and numeral 13 designates a header for distributing fuel into a plurality of fuel supply pipings 14. Fuel oil is supplied from the respective fuel supply pipings 14 to a plurality of fuel nozzles X2.
Numeral 60 designates an air control valve for leading a high pressure air into a wash tank 62 via a piping 61. The wash tank 62 stores therein the wash water for washing the interior of the compressor outlet 112. Numeral 63 designates an opening/closing valve, through which the wash water flows to be supplied into the manifold 113 via piping 64. The wash water supplied into the manifold 113 is injected from the plurality of wash nozzles 114 into the surrounding area for washing the interior of the compressor outlet 112. Numeral 65 designates an opening/closing valve and numeral 66 designates piping for supplying therethrough the wash water in a necessary quantity into the wash tank 62.
In the gas turbine compressor outlet wash system so constructed, when the compressor outlet 112 is to be washed, the air control valve 60 is opened and the high pressure air is led into the wash tank 62 via the piping 61 so that the interior of the wash tank 62 is pressurized. Then, the opening/closing valve 63 is opened and the wash water is supplied into the manifold 113 via the piping 64. The wash water is injected from the wash nozzles 114 for washing the interior of the compressor outlet 112.
On the other hand, as for the gas turbine operation, fuel oil is led into the header 13 via the flow control valve 11 and the piping 12 to be distributed there to flow into the plurality of fuel supply pipings 14 uniformly and is then supplied into the respective fuel nozzles X2 for combustion.
In the recent gas turbine, there is developed a dual fuel system in which both fuel oil and fuel gas are usable, and the fuel is changed over to gas from oil, or to oil from gas, as the case may be. In such a system, if for example, the operation done by oil is stopped or is continued with the fuel being changed over to gas from oil, the fuel oil remaining in the fuel pipings and nozzles is carbonized to stick there, and there arises a fear of blockage of the fuel pipings and nozzles. Thus, an attempt is being made for providing large scale facilities by which the fuel pipings and nozzles are purged by air or the like. But these exclusive purging facilities require a large apparatus, which is are naturally undesirable from the viewpoint of cost reduction.
In view of the problems in the prior art gas turbine fuel system, it is a principal object of the present invention to provide a gas turbine fuel system comprising a fuel oil supply system and a fuel gas supply system so that gas turbine operation may be performed with fuel being changed over to either oil or gas and further comprising a control system in which fuel is distributed to each fuel piping of the said fuel oil supply system uniformly in an appropriate flow rate and pressure as well as a purge system in which, while gas turbine operation is with gas fuel, residual oil in the fuel oil supply system is purged effectively by air or water so that the residual oil may not be carbonized.
In order to provide the gas turbine fuel system, the present invention has objects to provide following first to fourth systems.
First is a gas turbine fuel oil distribution control system in which a control valve is employed instead of a flow divider. The control valve is constructed such that differential pressure of each fuel nozzle is elevated at the initial time of gas turbine operation. Fuel oil is distributed so as to flow into each of fuel pipings connected to fuel nozzles as uniformly as possible so that an imbalance in fuel oil flow rate caused by a head difference between each fuel nozzle is resolved and any unusual elevation of the differential pressure at the time of a high fuel flow rate is prevented.
Second is a gas turbine fuel oil purge system in which, when gas turbine operation is with fuel being changed over to gas from oil and residual oil in fuel pipings and nozzles is to be purged, the quantity of the residual oil to be discharged into a combustor is made as small as possible and the residual oil is purged securely to be discharged.
Third is a gas turbine fuel nozzle purging air supply system in which compressor outlet air of about 400xc2x0 C. is cooled at a rotor cooling air cooler to an appropriate temperature to enter a pressure elevation compressor. Some coolers are thereby made unnecessary so that construction of the purging air supply system is simplified, installation space is reduced and the cost of facilities is reduced.
Fourth is a gas turbine fuel nozzle wash system in which existing gas turbine facilities may be used by being modified with a simple construction so that, when fuel is changed over to gas from oil, fuel nozzles are washed by water and residual oil in the fuel nozzles is washed out, resulting in a contribution to cost reduction of the gas turbine plant.
In order to realize the objects, the present invention provides the of following (1) to (5):
(1) A gas turbine fuel system comprises a fuel oil supply system for supplying fuel oil to a plurality of fuel nozzles and a fuel gas supply system for supplying fuel gas to the plurality of fuel nozzles so that gas turbine operation may be performed with fuel being changed over to either one of oil and gas. The system further comprises a fuel oil distribution control system for controlling flow rate and pressure of fuel oil in each of fuel pipings connecting to the fuel nozzles within a predetermined range by a control means provided in the fuel oil supply system, a fuel oil purge system provided close to the fuel nozzles in the fuel oil supply system for purging residual oil in the fuel oil supply system and fuel nozzles by air, a purging air supply system for supplying air to the fuel oil purge system, and a fuel nozzle wash system for supplying wash water to an upstream side of fuel nozzles in the fuel oil supply system connected to the fuel nozzles.
In the invention of (1) above, the fuel oil distribution control system causes fuel oil to flow into the fuel oil supply system uniformly so that any imbalance in the fuel flow rate in each of the pipings is resolved and the fuel oil purge system effectively purges the residual oil in the fuel oil supply system and fuel nozzles so that the problem of pipings being blocked by carbonization of the fuel oil is resolved. Also, the purging air supply system supplies air of an appropriate temperature into the purge system so that air supply to the purge system is ensured. Further, the fuel nozzle wash system purges the residual oil by injecting water so that reliability of purging the residual oil is enhanced. The air purge and water purge may be done by either of them being changed over to one from the other as the case may be.
(2) A gas turbine fuel oil distribution control system has a series control valve comprising a plurality of valves for controlling pressure loss in a fuel oil supply system so as to correspond to a plurality of fuel nozzles. Each of the plurality of valves is controllably driven at the same time with the same opening. A drive unit drives the series control valve. A control unit controls the drive unit, and said control unit is inputted with a system differential pressure signal and a load signal of the fuel oil supply system to put out to the drive unit a signal to throttle the series control valve approximately to an intermediate opening while the system differential pressure is a predetermined low differential pressure and a signal to open the series control valve fully for a predetermined time when said system differential pressure comes to a predetermined high differential pressure.
In the gas turbine fuel oil distribution control system of the invention of (2) above, while the series control valve is controlled in opening by the control unit and the drive unit, the control unit is inputted with a differential pressure signal and a load signal of the fuel oil supply system or the fuel nozzles to output to the drive unit a signal to throttle the series control valve approximately to an intermediate opening while the system differential pressure is a predetermined low differential pressure during the time from gas turbine ignition to rated speed arrival. In the high fuel flow rate area, when the system differential pressure comes to a predetermined high differential pressure, a signal to open the series control valve fully is output to the drive unit.
Thus, the differential pressure of each of the fuel nozzles is set to a higher differential pressure than the necessary nozzle differential pressure by the series control valve and the gas turbine operation is performed with the fuel oil being so controlled that imbalances in the fuel flow rate as so far occur in the low fuel flow rate area, are is reduced. Hence the prior art flow divider becomes unnecessary and the reliability of the fuel oil distribution is enhanced.
(3) A gas turbine fuel oil purge system in a gas turbine fuel oil supply system comprises a plurality of fuel oil supply pipings for supplying fuel oil to a plurality of fuel nozzles via a header. A drain piping is connected to the said plurality of fuel oil supply pipings. There is provided a sealing connection pipe close to the fuel nozzles in each of the fuel oil supply pipings between the header and fuel nozzles. A purging air supply piping supplies air to each sealing connection pipe, and each sealing connection pipe causes the air from the purging air supply piping to flow toward the fuel nozzles as well as to flow into the fuel oil supply pipings on the opposite side of the fuel nozzles to be discharged from the drain piping.
In the gas turbine fuel oil purge system of the invention of (3) above, the sealing connection pipe and the purging air supply piping are provided close to the fuel nozzles in each of the fuel oil supply pipings and air from the sealing connection pipe is injected from each of the fuel nozzles so that the residual oil only in the very short piping between the sealing connection pipe and each of the fuel nozzles is discharged into the combustor. At the same time, the combustion gas in the combustor is prevented from flowing reversely into the fuel oil supply pipings by the air injected from the fuel nozzles, hence the air so injected has sealing function as well.
During the sealing function, the air also flows from the sealing connection pipe into the fuel oil supply pipings on the opposite side of the fuel nozzles, and after flowing through the fuel oil supply pipings and the drain piping, it is discharged outside of the system. By this flow of air, all the residual oil in the fuel oil supply pipings is discharged outside of the system from the drain piping. According to the invention of (3) above, therefore, when the fuel is changed over to gas from oil and the residual oil in the pipings is to be purged, the residual oil to be injected into the combustor is only the residual oil in the very short piping close to the fuel nozzles and other residual oil is discharged outside of the system from the drain piping. Hence a load change caused by burning of the residual oil is reduced.
(4) A gas turbine fuel nozzle purging air supply system in a gas turbine air system supplies air, extracted from compressor outlet air and cooled at an air cooler, to a rotor as rotor cooling air, as well as supplying air, diverging from the air extracted from compressor outlet air and being elevated in pressure at a pressure elevation compressor, to be used as fuel nozzle purging air. The air cooler comprises a first cooler and a second cooler. Air cooled at the first cooler is used for the rotor cooling air and air diverging from the air cooled at the first cooler is sent to the second cooler to be cooled and then sent to the pressure elevation compressor.
In the gas turbine fuel nozzle purging air supply system of the invention of (4) above, the air cooler comprises the first and second coolers and the air cooled at the first cooler is used as the rotor cooling air to be supplied for rotor cooling. Further, a portion of the air cooled at the first cooler diverges to enter the second cooler to be cooled again, thus the compressor outlet air is cooled to a lower temperature and is led into the pressure elevation compressor. When the air is compressed to a higher pressure at the pressure elevation compressor, its temperature also is elevated, but as the air at the pressure elevation compressor inlet is sufficiently cooled to the lower temperature at the first and second coolers, even if it is elevated in temperature, it can be used as the fuel nozzle purging air without being cooled further.
In the prior art system, air extracted from the compressor outlet air is cooled at a separate cooler and is led into the pressure elevation compressor to be compressed and thus to be elevated in temperature. This air so elevated in temperature is cooled again at another separate cooler to be adjusted to a lower temperature, which is appropriate for the purging air. In the prior art system, therefore, separate coolers are needed and large facilities and space therefor are required. But in the invention of (4) above, the air cooler for the rotor cooling air is made in two units which are used for cooling the purging air as well, separate coolers are not needed, facilities are simplified and cost reduction is attained.
(5) A gas turbine fuel nozzle wash system in a gas turbine wash system comprises a fuel oil supply system for supplying fuel oil to fuel nozzles in a combustor. A compressor wash water supply system supplies wash water to a compressor which supplies compressed air to the combustor. A wash water tank supplies the wash water to the compressor wash water supply system. There are provided a wash water by-pass piping and an opening/closing valve between the fuel oil supply system and the compressor wash water supply system. When the opening/closing valve is opened, the wash water is supplied to the fuel nozzles from the wash water tank via the fuel oil supply system to be injected from the fuel nozzles so that the fuel nozzles are washable.
In the gas turbine fuel nozzle wash system of the invention of (5) above, the wash water by-pass piping and the opening/closing valve are provided between the existing fuel oil supply system and the compressor outlet wash system so that the wash water for compressor washing in the wash water tank is led into the fuel oil supply system. When the fuel is changed over to gas from oil, the oil remains in the fuel nozzles and is carbonized to stick there, which results in a fear of blockage of the fuel nozzles. Hence, when the fuel is changed over to gas, wash water for the compressor washing is led to the fuel nozzles via the wash water by-pass piping and fuel oil supply system to be injected from the fuel nozzles. Thus, the fuel nozzles are washed and a fear of blockage of the nozzles is resolved. Accordingly, the existing pipings are made use of and wash water for the compressor washing is used for nozzle washing as well, whereby facilities cost is reduced and washing of the fuel nozzles with a simple structure becomes possible.